Polarization plane switch and optical switching device using the same

Abstract

A polarization plane switch comprising a Faraday rotator made of an iron-containing garnet single-crystal film and magnetic field applying devices capable of reversing a magnetic field to be applied to the Faraday rotator. The polarization plane switch has a structure in which magnetization of part of the Faraday rotator is unsaturated and that of the remaining portion of it is saturated when a magnetic field is applied to the Faraday rotator by the magnetic field applying device, and a light beam passes through the magnetically saturated portion almost vertically to the film surface. As the above Faraday rotator, it is the most preferable to use a Faraday rotator made of Bi-substituted iron garnet single crystal formed by liquid-phase epitaxy and having a compensation temperature, and thermally treated under the top condition at a temperature between 1,120 DEG and 1,180 DEG C. for 7 hours or less.

What is claimed is: 
     
       1. A polarization plane switch comprising a yoke made of a magnetic material, a coil provided on the yoke, and a flat Faraday rotator inserted into a gap formed on the yoke vertically to the longitudinal direction of the gap, wherein the Faraday rotator is made of a Bi-substituted iron garnet single-crystal film formed by liquid-phase epitaxy and having a compensation temperature, and thermally treated under the top condition at a temperature between 1,120° and 1,180° C. for 0.5 to 7 hours. 
     
     
       2. The polarization plane switch according to claim 1, wherein the Faraday rotator has such a size that it protrudes outside the gap and a light beam passes through the protruding portion almost vertically to the plane of the single-crystal film. 
     
     
       3. The polarization plane switch according to claim 2, wherein the protruding portion is provided with a magnetic shielding material to form a magnetically unsaturated region and a light beam passes through a magnetically saturated region of the protruding portion almost vertically to the film surface. 
     
     
       4. A polarization plane switch comprising: a yoke made of magnetic material;   a coil provided on the yoke;   a flat Faraday rotator inserted into a gap formed on the yoke vertically to the longitudinal direction of the gap said Faraday rotator being made of an iron-containing garnet single-crystal film; and   magnetic field applying means capable of reversing magnetic field to be applied to the Faraday rotator,   wherein said Faraday rotator has a protruding portion protruding outside said gap, and said Faraday rotator has a magnetically unsaturated portion and a magnetically saturated portion when the magnetic field is applied to the Faraday rotator, so that a light beam passes through the projecting portion almost vertically to the plane of said single-crystal film.   
     
     
       5. A polarization plane switch comprising a main yoke and an auxiliary yoke which are made of a magnetic material, a coil provided on the both yokes respectively, and an iron-containing garnet single crystal inserted into gaps formed on the both yokes in common vertically to the longitudinal direction of the gaps, wherein a magnetic field generated by the main yoke and a magnetic field generated by the auxiliary yoke are applied to the Faraday rotator from the opposite direction to each other and a light beam passes through the magnetically saturated region formed by the main yoke of the Faraday rotator almost vertically to the film surface. 
     
     
       6. A polarization plane switch comprising a yoke made of a magnetic material, a coil provided on the yoke, and a Faraday rotator made of an iron-containing garnet single-crystal film inserted into a gap formed on the yoke vertically to the longitudinal direction of the gap, wherein a plurality of portions with a small gap length are formed on the gap of the yoke portions of the Faraday rotator corresponding to the portions with the small gap length serve as magnetically saturated regions and other portions of the Faraday rotator serve as magnetically unsaturated regions, and a light beam passes through the magnetically saturated regions almost vertically to the film surface. 
     
     
       7. An optical switching device comprising: two wedge-shaped birefringent single-crystal devices arranged so as to face each other;   a Faraday rotator arranged between the two single-crystal devices;   magnetic field applying means for reversing a magnetic field applied to the Faraday rotator;   optical fiber means for input; and   optical fiber means for output; wherein   the Faraday rotator is made of a Bi-substituted iron garnet single-crystal film formed by liquid-phase epitaxy and having a compensation temperature, and thermally treated under the top condition at a temperature between 1,120° and 1,180° C. for 0.5 to 7 hours.   
     
     
       8. A polarization plane switch comprising: a Faraday rotator made of Bi-substituted iron garnet single-crystal film formed by liquid-phase epitaxy and having a compensation temperature, and thermally treated under the top condition at a temperature between 1,120° and 1,180° for 0.5 to 7 hours; and   magnetic field applying means for applying a magnetic field to the Faraday rotator; wherein   the single crystal is made of (GdBi) 3  (FeAlGa) 5  O 12 .